The zeolite P class includes a series of synthetic zeolite phases which may be in cubic configuration (also termed B or Pc) or tetragonal configuration (also termed P1) but is not limited to these forms. The structure and characteristics of the zeolite P class are given in "Zeolite Molecular Sieves" of Donald W Breck (published 1974 and 1984 by Robert E Krieger of Florida U.S.A.). The zeolite P class has the typical oxide formula: EQU M.sub.2/n O. Al.sub.2 O.sub.3. 1.80-5.00SiO.sub.2. 5H.sub.2 O
M is an n-valent cation which for this invention is an alkali metal, that is lithium, potassium, sodium, caesium or rubidium with sodium and potassium being preferred and sodium being the cation normally used in commercial processes.
Thus sodium may be present as the major cation with another alkali metal present in a minor proportion to provide specific benefit.
In the present invention crystalline P-zeolites having a Si:Al ratio from 0.9 to 1.33 are used.
The utility of zeolites P in detergents formulations has been acknowledged. For example, European Patent Application 0384070 (Unilever) discloses the use of a specific zeolite P as detergency builders.
In EP0384070, comparisons of calcium binding capacity and calcium uptake rate are made between the specific zeolite P which is disclosed in that document and zeolite 4A.
It has now been found that certain zeolites P prove to have, at a temperature as low as 5.degree. C., a very high calcium binding capacity as well as a very good rate of calcium ion uptake. Therefore, those materials are very useful as calcium binders when used at low temperature, i.e. below 25.degree. C. Specifically, those materials are useful in detergents compositions which are used at ambient temperature.